Auditory fear conditioning, a learning paradigm in which a rat can form an association between a previously neutral tone and a painful stimulus, is believed to occur via the persistent strengthening of synaptic connections, termed long-term potentiation (LTP), in the lateral amygdala (LA). Protein synthesis is necessary for both consolidation and reconsolidation of fear conditioning memory, and this may suggest a role for synapse remodeling. Auditory information enters the LA via plastic synapses from both the thalamus and cortex, but the functional and anatomical relationship between these synapses is unclear. The proposed project will begin to investigate the relative roles of these synapses in fear conditioning memory and their structural underpinnings. First, the protein synthesis-dependence of LTP consolidation and reconsolidation will be compared between the cortical and thalamic input pathways using a behaviorally relevant induction protocol. Second, serial section electron microscopy will be used to examine ultrastructural changes in LA synapses that occur during consolidation of fear conditioning and LTP, including changes in synapse size, synapse number, and local protein synthesis. Tracer injections will allow comparison of cortical and thalamic synapses under all conditions. A better understanding of the synaptic basis of the formation and maintenance of fear memories is important for the development of interventions for psychiatric disorders involving fear associations, such as phobias.